Lubricant blend and use of the same

ABSTRACT

Novel lubricant mixtures suitable for external lubrication in interior high-pressure forming and their methods of use are disclosed.

CROSS-REFERENCE TO RELATED APPLICATION

[0001] This application is a U.S. National Phase entry of PCT/EP01/12462, filed on Oct. 27, 2001, claiming priority of DE 101 15 696.0, filed on Mar. 29, 2001.

FIELD OF THE INVENTION

[0002] This invention relates to a lubricant mixture which may be used for lubrication between work piece and mould during the non-cutting shaping of metal work pieces. It is particularly suitable for external lubrication in interior high-pressure forming.

BACKGROUND OF THE INVENTION

[0003] During the non-cutting shaping of metal work pieces, the work piece is subjected to a force, the result of which is the forming of the metal by flow processes. Examples of these are forming by pressing, cold extrusion, drawing, deep drawing as well as interior high-pressure forming (“IHP”), internationally referred to in English as “hydroforming”. In these processes, friction arises between the surface of the work piece and the mould employed, such moulds including for example, mould cavities, punches, drawing moulds, drawing dies or, in the case of IHP, the hollow mould. It is necessary to reduce this friction by using a suitable lubricant or there may be damage to the mould or work piece, for example, through cold welding. Moreover, the lubricant decreases the force and the expenditure of energy which are required for the forming process.

[0004] IHP, for which the lubricant according to the invention is particularly suitable, is a forming process whereby hollow metal parts are formed in a mould by means of a liquid medium (“pressure intensifier”). (See, for example: the paper by Dieter Brans, “Tribologische Aspekte beim Innenhochdruckumformen”, Symposium “Metallbearbeitung heute und morgen” of the Verband Schmierstoff-Industrie, Frankfurt/Main, 2nd and 3rd Nov. 1998, and Christian Busch, Rainer Dörfler, Wolfgang Buβ and Christoph Metz, “Schmierungskonzepte für IHU-Werkstücke und Druckfluide für den IHU-Prozeβ”, paper at the Automobil Arbeitskreis Umformen, Bad Nauheim, 30th Nov. 1999, and the literature cited therein. IHP and an external lubricant which can be used for the process are also the subject matter of WO 00/13814.)

[0005] In IHP, a liquid pressure medium is used in order to build up an internal pressure in a hollow-body work piece. Depending on parts geometry, work piece properties, and material thickness, the pressure may be in the range of about 800 to about 10,000 bar. In addition to forces arising from the pressure medium, other mechanical forces which bring about additional flow of work piece material into the shaping zone may be used. These additional forces may act in an axial or radial direction and are of the order of about 800 to about 3000 bar.

[0006] IHP is conventionally carried out in the following steps (see D. Brans cited herein supra): 1) the work piece is placed in the mould; 2) the hydraulic cylinder is connected; 3) the interior of the work piece is filled with the pressure medium and then de-aerated; 4) the required internal forming pressure is built up by a pressure intensifier; 5) the internal pressure is increased to “calibration pressure” (for example, up to 8000 bar) when the work piece dimensions approach that of its desired final contours, 6) the work piece fills the cavity of the mould; and subsequently 6) the pressure is decreased and the pressure medium is discharged.

[0007] During this forming, there is a relative movement between work piece and mould and hence a friction between their surfaces. It is therefore necessary to apply a lubricant between work piece and mould. This is also referred to as “external lubrication” or “external lubricant” (internationally by the English term “die-side lube.

[0008] Traditionally, examples of external lubricants have included (see the literature cited above) drawing lubricants and drawing greases, soaps on conversion layers such as, for example, phosphating or oxalating layers, non-stick paints containing graphite, molybdenum sulfide or Teflon, waxes and drawing sheets.

[0009] Disadvantages of these prior art products may include: limitations with regard to their application, requirement for cost-intensive conversion treatment, performance deterioration, contamination of the end product, difficulty of removal at the end of the forming process, particulate-caused blockage of the very fine pressure intensifier filters, and cost-in-use.

[0010] Suitable pressure media” (internationally referred to in English as “pressure-side lube”) include hydraulic oils (use is limited, owing to their compressibility to pressures of below about 1500 bar) and aqueous media based on water-miscible products containing mineral oils or on synthetic solutions, which are also known in the field of cooling lubricants.

[0011] In theory the pressure medium and external lubricant remain separate throughout the forming process. In practice, however, the external lubricant may be introduced into the pressure medium, or the external lubricant may become contaminated by the pressure medium. Either of these may cause inadequate lubricating action. Should these or similar events occur, it is desirable that the two media have the capability to rapidly and independently separate from one another. This property allows the possibility for the independent reuse of pressure medium or external lubricant and thereby may reduce production costs.

[0012] There is still an unfilled need for lubricant mixtures that may be used for lubrication between work piece and mould during the non-cutting shaping of metal work pieces, particularly for external lubrication in interior high-pressure forming. The present invention is related to these and other important ends.

SUMMARY OF THE INVENTION

[0013] The present invention is generally directed to lubricant mixtures and methods of their use.

[0014] Accordingly, the present invention relates in part to a method for lubricating between a mould and a work piece to be formed under high pressure in the mould, comprising contacting the mould and the work piece with a lubricant mixture comprising from about 40% to about 99.6% by weight of the mixture of at least one oil which is liquid at room temperature; and from about 0.4% to about 10% by weight of the mixture of at least one wax.

[0015] The invention also relates in part to a lubricant mixture for use in high-pressure forming of a metal work piece in a mould, comprising from about 40% to about 99.6% by weight of the mixture of at least one oil which is liquid at room temperature; and from about 0.4% to about 10% by weight of the mixture of at least one wax.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

[0016] As employed above and throughout the disclosure, the following terms, unless otherwise indicated, shall be understood to have the following meanings.

[0017] As used herein, “oil” refers to a substance which is liquid at room temperature, has a viscosity greater than that of water under identical conditions and is not miscible with water. Non-limiting examples include paraffin- or napthene-based mineral oils, natural oils (i.e. vegetable or animal), and synthetic ester oils. Preferably, the oils are mineral oils. In other preferred embodiments, the oils have a viscosity in the range of 2 to 500 mm²/second at 20° C., measured in accordance with DIN 53211. Preferably, the lubricant mixture contains at least about 55% by weight of the mixture, more preferably at least about 60% by weight of the mixture and even more preferably at least about 70% by weight of the mixture of oil.

[0018] As used herein, “wax” refers to natural waxes, modified waxes or synthetic waxes. Non-limiting examples include montan wax, camauba wax and polyethylene wax. Preferably, the lubricant mixture contains at least about 0.4% wax by weight of the lubricant mixture, and more preferably, at least about 0.6% wax by weight of the mixture. Preferably, the wax content is up to about 5% by weight of the mixture, and more preferably, up to about 3% by weight of the lubricant mixture. In some preferred embodiments, a mixture of waxes may be used. As a non-limiting example, montan wax may be used as a wax mixture with polyethylene wax.

[0019] As used herein, “lubricant additive” refers to a high-performance lubricant additive (so-called “EP additives”, after the English term “extreme-pressure additive”), which includes, for example, sulfur- or phosphorus-containing EP additives. Non limiting examples of EP additives include sulfur-containing fatty acid esters, dialkyl trisulfides, dialkyl pentasulfides, for example “di-tert.-dodecyl polysulfide”, which appears to be mainly the trisulfide, and neutralised phosphoric esters.

[0020] As used herein, “fatty acid ester” refers to an ester derivative of a long chain fatty acid, the fatty acid portion of the ester having from about 8 to about 22 carbon atoms. Preferably, the fatty acid has from about 12 to about 18 carbon atoms. In another preferred embodiment, the fatty acid esters are derived from vegetable or animal sources, esterified with monohydric or polyhydric, preferably polyhydric alcohols having 2 to 6 carbon atoms. Even more preferably, the polyhydric alcohol component of the ester is glycerol, trimethylolpropane or pentaerythritol, wherein at least one of the alcohol's hydroxy groups is esterified with fatty acid. Non-limiting examples include trimethylolpropane trioleate, glycerol tricaprylate and dipentaerythritol fatty acid ester.

[0021] As used herein, “emulsifier” refers to a compound having surfactant properties such as, for example, soaps, alkyl sulfates or alkyl sulfonates or alkoxylation products of alcohols, amines and carboxylic acids [alkyl-C(═O)-OH] having 7 or more carbon atoms in the alkyl group. In practice, reduced levels of emulsifiers facilitate the separation of co-mingled pressure medium and lubricant mixture of the invention. In some preferable embodiments the emulsifier comprises up to about 1% by weight of the lubricant mixture. More preferably the emulsifier comprises up to about 0.5% by weight of the mixture. Even more preferably, the emulsifier comprises up to about 0.1% by weight of the lubricant mixture. In a particularly preferred embodiment, no emulsifiers are intentionally added to the lubricant mixture.

[0022] Accordingly, in one embodiment, the invention relates to a method for lubricating between a mould and a work piece to be formed under high pressure in the mould, comprising contacting the mould and the work piece with a lubricant mixture comprising from about 40% to about 99.6% by weight of the mixture of at least one oil which is liquid at room temperature; and from about 0.4% to about 10% by weight of the mixture of at least one wax. Preferably, the lubricant mixture further comprises from about 1% to about 25% by weight of the mixture of at least one fatty acid ester, lubricant additive, or mixture thereof. Even more preferably, the lubricant mixture of the above method further comprises a mixture of at least one fatty acid ester and at least one lubricant additive.

[0023] In some preferred embodiments, the lubricant mixture is a liquid at room temperature. In other preferred embodiments, the lubricant mixture is in the form of a paste at room temperature.

[0024] In yet other preferred embodiments, the lubricant mixture is applied to the interior surface of the mould or to the exterior surface of the work piece by spraying, airless spraying, dipping, roller application or brushing.

[0025] In some preferred embodiments, the high-pressure forming of said work piece is effected using a liquid pressure medium. More preferably, the liquid is water-based. More preferably still, upon completion of the high-pressure forming process of the work piece, a phase separation between the lubricant mixture and the pressure medium occurs. Even more preferably, upon completion of the high-pressure forming process of the work piece, at least part of the lubricant mixture is removed from the work piece or the mould with a water-based cleaning medium.

[0026] In other more preferred embodiments, the invention relates to a method for lubricating between a mould and a work piece to be formed under high pressure in the mould, comprising contacting the mould and the work piece with a lubricant mixture comprising from about 40% to about 84.6% by weight of the mixture of at least one oil which is liquid at room temperature; from about 0.4% to about 10% by weight of the mixture of at least one wax, and from about 1% to about 25% by weight of the mixture of at least one fatty acid ester, lubricant additive, or mixture thereof. More preferably still, the fatty acid ester, lubricant additive, or mixture thereof comprises at least about 15% by weight of the lubricant. Even more preferably, the lubricant mixture comprises from about 50% to about 84.6% by weight of the mixture of at least one oil which is liquid at room temperature; from about 5% to about 20% by weight of the mixture of at least one fatty acid ester; and from about 5% to about 20% by weight of the mixture of at least one lubricant additive.

[0027] In one embodiment, the invention provides a novel lubricant mixture which can be used for external lubrication in IHP as well as for other non-cutting shaping processes. Preferably the lubricant mixture is readily applied. In other embodiments, the lubricant mixture is removed from the work piece or mould, at least in part, with a water-based cleaning system.

[0028] In certain embodiments, the invention provides a pressure medium and a lubricant mixture which, when co-mingled, rapidly separate from each other, and may be independently reused.

[0029] In one embodiment, the invention relates to a lubricant mixture for use in high-pressure forming of a metal work piece in a mould, comprising from about 40% to about 99.6% by weight of the mixture of at least one oil which is liquid at room temperature; and from about 0.4% to about 10% by weight of the mixture of at least one wax. Preferably, the lubricant mixture further comprises from about 1% to about 25% by weight of the mixture of at least one fatty acid ester, lubricant additive, or mixture thereof. Even more preferably, the fatty acid ester, lubricant additive, or mixture thereof comprises at least about 15% by weight of the lubricant mixture.

[0030] It is believed that the waxes are liquefied by the oil when used in the proportions provided herein and improve the lubricating action of the oil, leading to a very low coefficient of friction. In some embodiments, the oil-wax mixture is readily removed from the surfaces covered with them by means of conventional aqueous cleaning agents. In the case of an unintentional, but frequently unavoidable, introduction of the lubricant mixture into the pressure medium, the use of the lubricant mixtures herein reduce the risk of clogging the very fine filters associated with the pressure intensifiers.

[0031] The lubricant mixture preferably has a low water content and more preferably is substantially free of water. That is, preferably no water is intentionally added to the lubricant mixture. In practice, however, a limited entry of water cannot always be avoided. Typically, he lubricant mixture comprises up to about 5 wt. % by weight, preferably up to about 1 wt. % by weight, and more preferably up to about 0.5 wt. % by weight of water in the lubricant mixture.

[0032] The viscosity of the lubricant mixture can be adjusted over a wide range, so that at room temperature (15° C. to 25° C.) the lubricant mixture can be liquid or in the form of a paste. This facilitates the application of the lubricant mixture to the work piece or the mould. For example, the viscosity at 20° C., measured in accordance with DIN 53211, may be in the range of 10 to 5000 mM²/second, in particular 20 to 2000 mm²/second. In this connection, viscosities in the range of 10 to 200 mm²/second are preferred for spray applications.

[0033] The lubricant mixture is used preferably for lubrication between work piece and mould during the non-cutting shaping of metal work pieces. The lubricant mixture is preferably employed during interior high-pressure forming for the purpose of external lubrication, that is, for lubrication between work piece and mould.

EXAMPLES

[0034] The disclosures of each patent, patent application and publication cited or described in this document are hereby incorporated herein by reference, in their entirety.

[0035] Those skilled in the art will appreciate that numerous changes and modifications can be made to the preferred embodiments of the invention and that such changes and modifications can be made without departing from the spirit of the invention. It is, therefore, intended that the appended claims cover all such equivalent variations as fall within the true spirit and scope of the invention. TABLE 1a Examples of particularly preferred lubricant mixtures according to the invention (prepared by mixing the individual components together in the given order) Type of Name of raw Ex. Ex. Ex. Ex. constituent material a) b) c) Ex. e) Mineral oil Nynas T 9 79.2 — — 79.2 74.7 (viscosity Shell Gravex 921 — 79.2 — at 40° C. Nynas T 110 — — 79.2 in mm²/sec) Nynas T 400  9  21 110 400 Fatty acid ester Edenor 3237 10.0 10.0 10.0 10 10 (Dipentaerythritol fatty acid ester) EP additive Di-tert. dodecyl 10.0 10.0 10.0 10 10 polysulfide Polyethylene Licowachs PE 810  0.3  0.3  0.3 0.3 0.3 wax Montan wax Licowachs OP  0.5  0.5  0.5 0.5 5.0

[0036] TABLE 1b Examples of other lubricant mixtures according to the invention Ex. Ex. Ex. Ex. Ex. Raw material f) g) h) i) j) Shell Gravex 921 89.2 89.2 99.2 99.2 99.2 Edenor 3237 — 10.0 — — — Di-tert. dodecyl polysulfide 10.0 — — — — Licowachs PE 810  0.3  0.3  0.3  0.8 — Licowachs OP  0.5  0.5  0.5 —  0.8

[0037] The coefficient of friction was determined by the so-called cylinder test: A cylinder (diameter: 5 cm, length: 12 cm, material: steel St 35), to which the cooling lubricant is applied (manually, by wiping), is pushed 7.5-12 cm through a tube of equal diameter (tool steel No. 12379) under a pressure of 800 bar. The resulting frictional force Fr is measured as a function of the motion; it correlates linearly with the coefficient of friction.

Fr=C.o.F×R×pi×I×p

[0038] C.o.F: coefficient of friction

[0039] pi: 3.14159 . . .

[0040] R: radius

[0041] I: length

[0042] p: pressure

[0043] Table 2a and Table 2b show the coefficient of friction, measured at half the length of the path. In the experiment involving contact with pressure-side lube, a dilute solution of a pressure-side lube was sprayed onto the wax-containing die-side lubes, in order to simulate conditions in practice. TABLE 2a Coefficient of friction of lubricant mixtures according to the invention Ex. Ex. Ex. Ex. Ex. Measured results a) b) c) d) e) Viscosity in mm²/sec 53 127 844 highly highly (DIN 53211, 20° C.) viscous viscous Coefficient of friction 0.013 0.015 0.017 0.010 0.011 (at half the measured length) without contact with 0.010 0.008 0.003 0.011 0.011 pressure-side fluid (= pressure medium) after contact with pressure-side fluid

[0044] TABLE 2b Coefficient of friction of other lubricant mixtures of the invention Ex. Ex. Ex. Measured results f) g) h) Ex. i Ex. j Coefficient of friction 0.0128 0.0126 0.0124 0.0120 0.0128 (at half the measured length) without contact with 0.0106 0.0115 0.0120 0.0110 0.0115 pressure-side fluid (= pressure medium) after contact with pressure-side fluid

[0045] The separation of die-side lube and pressure-side lube was carried out in accordance with DIN 51599, in combination with the assessment system of the firm of Hans Schmidt Gleittechnik (“Demulgierverhalten von Bettbahnölen und Kühlschmierstoffen”, obtainable from Hans Schmidt Gleittechnik GmbH & Co. KG, Schloβgrund 15, 96472 Rödental, Germany). The results are shown in Table 3.

[0046] Pressure-side lubes: (in each case 5% solutions)

[0047] P3-multan® 70-40

[0048] semi-synthetic cooling lubricant containing emulsifiers (anionic/non-ionic)

[0049] P3-multan® 61-2 DF

[0050] wholly synthetic cooling lubricant without non-ionic surfactants

[0051] (The above products are commercial products of Henkel KGAA)

[0052] Die-side lubes (=external lubricant):

[0053] according to the invention and emulsifier-free:

[0054] Examples a, b and c

[0055] emulsifier-containing: (not according to the invention)

[0056] Michem® Lube 160 (camauba wax containing emulsifier, commercial product of the firm of Michelman Inc., Cincinnati, Ohio, USA)

EXPERIMENTAL PROCEDURE

[0057] Four parts by weight of pressure-side lube was vigorously shaken ten times together with one part by weight of die-side lube in a reagent flask and subsequently left to stand.

[0058] Assessment:

[0059] 1: complete phase separation

[0060] 2: almost complete phase separation

[0061] 3: 3 phases: oil, aqueous solution and foam

[0062] 4: oil and foam phase

[0063] 5: no phase separation TABLE 3 Results of the experiments on phase separation P3-multan ® 61-2 DF P3-multan ® 70-40 After 1 minute Example a) 2 4 Example b) 1 2 Example c) 1 3 Michem ® Lube 160 5 5 After 10 minutes Example a) 1 2 Example b) 1 2 Example c) 1 2 Michem ® Lube 160 5 5 Aqueous phase appearance/height (cm) appearance/height (cm) Example a) clear/1.95 turbid/1.4 Example b) clear/1.65 turbid/1.4 Example c) clear/1.6 turbid/1.4 Michem ® Lube 160 No phase separation No phase separation

[0064] The results show that aqueous wax emulsions containing emulsifier are unsuitable for use as die-side lubes and that semi-synthetic cooling lubricants are less suitable than are wholly synthetic cooling lubricants for use as pressure-side lubes.

[0065] The removability using cleaning agents was tested in the following way: 0.2 ml of each of Examples a, b, c was applied to an iron strip having a surface area of 30 cm2 and stored for 24 hours in a drying oven at 65° C. The strips were then cleaned in a 10 l spray booth, using 20 g/l P3-neutracare® 310 (Henkel KGaA) in industrial water at a pressure of 2.5 bar at 65□C for 2 minutes, and subsequently rinsed with deionised water. In all three Examples, the residual carbon content was less than 2 percent of the initial value. 

What is claimed:
 1. A method for lubricating between a mould and a work piece to be formed under high pressure in the mould, comprising: contacting the mould and the work piece with a lubricant mixture comprising: from about 40% to about 99.6% by weight of the mixture of at least one oil which is liquid at room temperature; and from about 0.4% to about 10% by weight of the mixture of at least one wax.
 2. The method of claim 1, wherein the lubricant mixture further comprises: from about 1% to about 25% by weight of the mixture of at least one fatty acid ester.
 3. The method of claim 1, wherein the lubricant mixture further comprises: from about 1% to about 25% by weight of the mixture of at least one lubricant additive.
 4. The method of claim 2, wherein the lubricant mixture further comprises: from about 1% to about 25% by weight of the mixture of at least one lubricant additive.
 5. The method of claim 4, wherein the lubricant mixture comprises: from about 40% to about 84.6% by weight of the mixture of oil; and at least about 15% by weight of the mixture of at least one fatty acid ester, or at least one lubricant additive, or mixture thereof.
 6. The method of claim 1 wherein the lubricant mixture further comprises up to about 5% by weight of water.
 7. The method of claim 1, wherein the lubricant mixture further comprises up to about 1% by weight of emulsifier.
 8. The method of claim 7 wherein the emulsifier comprises up to about 0.1% by weight of the mixture.
 9. The method of claim 5, wherein the lubricant mixture comprises: from about 50% to about 84.6% by weight of the mixture of at least one oil which is liquid at room temperature; from about 5% to about 20% by weight of the mixture of at least one fatty acid ester; and from about 5% to about 20% by weight of the mixture of at least one lubricant additive.
 10. The method of claim 1, wherein the lubricant mixture is a liquid at room temperature.
 11. The method of claim 1, wherein the lubricant mixture is in the form of a paste at room temperature.
 12. The method of claim 1, wherein the lubricant mixture is applied to the interior surface of the mould or to the exterior surface of the work piece by spraying, airless-spraying, dipping, roller application or brushing.
 13. The method of claim 1, wherein the high-pressure forming of said work piece is effected using a liquid, pressure medium.
 14. The method of claim 13, wherein the liquid is water based.
 15. The method of claim 14, wherein upon completion of the high-pressure forming process of the work piece, a phase separation between the lubricant mixture and the pressure medium occurs.
 16. The method of claim 14, wherein upon completion of the high-pressure forming process of the work piece, at least part of the lubricant mixture is removed from the work piece or the mould with a water-based cleaning medium.
 17. A lubricant mixture for use in high-pressure forming of a metal work piece in a mould, comprising: from about 40% to about 99.6% by weight of the mixture of at least one oil which is liquid at room temperature; and from about 0.4% to about 10% by weight of the mixture of at least one wax.
 18. A lubricant mixture of claim 17 further comprising from about 1% to about 25% by weight of the mixture of at least one fatty acid ester.
 19. The lubricant mixture of claim 17 further comprising from about 1% to about 25% by weight of the mixture of at least one lubricant additive.
 20. The lubricant mixture of claim 18 further comprising from about 1% to about 25% by weight of the mixture of at least one lubricant additive.
 21. The lubricant mixture of claim 20 wherein the fatty acid ester, or the lubricant additive, or mixture thereof comprise at least about 15% by weight of the lubricant mixture. 